1. Field of the Invention
The present general inventive concept relates to an image forming apparatus and a method thereof. More particularly, the present general inventive concept relates to an image forming apparatus and concomitant method in which different path resistances are selected according to printing media so that residual charge is properly eliminated from a printing medium.
2. Description of the Related Art
Various types of image forming apparatuses are available, and are mainly categorized by printing method as a dot printer, an inkjet printer, and a laser printer. Laser printers are generally considered to be superior to dot printers and inkjet printers due to their faster printing speed and better printing quality. Therefore, image forming apparatuses applying a laser printing method are widely used.
An image forming apparatus using the laser printing method generally operates through the operations of primary charge, exposure, development, transferring, and fusing. In the primary charge operation, a negative charge is applied to a surface of an organic photo conductive unit (OPC). The charge on the OPC may be locally altered by an application of light, and, in the exposure operation, a latent image is written to the OPC, which may define a surface of a drum, via a laser beam from a laser scanning unit (LSU). In the development operation, a charged toner is affixed to the latent image to develop a visual image. In the transferring operation, the toner image is transferred to a printing medium, and, in the fusing operation, the toner image is bonded to the printing medium by heat and pressure. The printing operation is then complete.
In the transferring operation, a printing medium retains charge from a transfer voltage and passes through a nip between a transfer-charging roller and an OPC, and a gap is generated between the OPC and the printing medium. The toner jumps the gap through a potential difference between the OPC and the printing medium. If a subsequent transfer operation is to be performed on the same printing medium, excessive charge thereon may, along with other problems occurring from excessive static charge accumulating between charged surfaces, prevent the proper transfer of toner in the subsequent image transfer process such that a color image of low toner density results.
A static electricity eliminator is used to prevent the foregoing problems. The static electricity eliminator removes the residual charge from the printing medium. Generally, if an image is printed in low moisture conditions, on a printing medium of high resistance composition, or on both sides of a printing medium, the printing medium presents a high resistance between the transfer-charging roller and the OPC. As a result, charge on the transfer-charging roller applied to attract toner to the latent image may be leaked as a current to the static electricity eliminator through a transfer belt.
An image forming apparatus having a resistor between a static electricity eliminator and a ground has been suggested to alleviate the transfer current leakage problems. FIG. 1 is a schematic diagram illustrating an interior of such an image forming apparatus to perform static electricity elimination.
Referring to FIG. 1, a conventional image forming apparatus comprises an organic photo conductive unit (OPC) 10, a transfer roller 20, a static electricity eliminator 30, a resistor 40, a driving roller 50, and a transfer belt 60. The image forming apparatus charges the transfer-charging roller 20 when a printing medium is transferred thereto on the transfer belt 60 as driven by a driving roller 50. A current flowing to the transfer-charging roller 20 charges the printing medium to attract toner on the OPC 10. However, when the printing medium presents a high resistance in the charge transfer path, the current that would normally flow to charge the printing is diverted across the transfer belt to the static electricity eliminator 30. If the static electricity eliminator 30 is grounded through the resistor 40, the path of least resistance will be into the printing medium. By way of the resistor 40, the image forming apparatus prevents current from leaking through the transfer belt 50.
Accordingly, better static electricity elimination is provided since charge carried over the transfer belt 50 is prevented from interfering with the operation of the static electricity eliminator 30, particularly when images are printed on the printing media having high resistance, or on the both sides of a printing medium. However, resistance between the static electricity eliminator and ground hinders current from flowing, and when images are printed on general purpose paper or on a single side of a printing medium, the added resistance to ground is not needed to prevent the leakage current across the transfer belt 60. Consequently, the conventional image forming apparatus has a problem that residual charge is not completely eliminated in low resistance printing medium situations.
As explained above, the operation of a static electricity eliminator and printing quality are influenced by the resistance and condition of the printing medium. Additionally, limited operations are provided to a user, because of limited compatibly of certain printing operations and image forming apparatuses with certain paper types.